CMake: Detecting External Libraries – Using pkg-config

Introduction:

In the previous articles, we have basically understood how to link a third-party library. This article and the next will supplement two methods for detecting external libraries.

So far, we have learned two methods for detecting external dependencies:

• Using the built-in CMake find-module, but not all packages can be found in the CMake find module.

• Using <package>Config.cmake, <package>ConfigVersion.cmake, and <package>Targets.cmake, which are provided by the package vendor and installed in the standard cmake folder with the package.

If a dependency does not provide a find module or vendor’s CMake files, in this case:

• Depend on the pkg-config program to find packages on the system. This relies on the package vendor’s .pc configuration file, which contains metadata about the release package.

• Write your own find-package module for the dependency.

Next, we will demonstrate the use of the first method through ZMQ.

✦

Installation of ZMQ

✦

Download ZMQ:

https://github.com/zeromq

After downloading, extract it and enter the directory:

tar -xzvf  libzmq-4.3.4.tar.gz .

cd libzmq-4.3.4

Start the installation

./autogen.sh

Use prefix to specify the installation directory

./configure --prefix=/opt/zmq/ --without-libsodium
make
sudo make install

✦

Project Structure

✦

.
├── CMakeLists.txt
├── zmq_client.cpp
└── zmq_server.cpp

Project address:

https://gitee.com/jiangli01/tutorials/tree/master/cmake-tutorial/chapter3/05

✦

CMakeLists.txt

✦

cmake_minimum_required(VERSION 3.10 FATAL_ERROR)

project(test_zmq LANGUAGES CXX)

set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_EXTENSIONS OFF)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_PREFIX_PATH /opt/zmq)

find_package(PkgConfig REQUIRED QUIET)

pkg_search_module(
  ZeroMQ
  REQUIRED libzeromq libzmq lib0mq
  IMPORTED_TARGET
)

if(TARGET PkgConfig::ZeroMQ)
    message(STATUS "Found ZeroMQ")
endif()

add_executable(hw_server zmq_server.cpp)
target_link_libraries(hw_server PkgConfig::ZeroMQ)

add_executable(hw_client zmq_client.cpp)
target_link_libraries(hw_client PkgConfig::ZeroMQ)

Use pkg_search_module to search for any libraries or programs that come with a .pc file to find and import the ZeroMQ library. This command will find and configure the ZeroMQ library in CMake using the PkgConfig tool.

pkg_search_module(
  ZeroMQ
  REQUIRED libzeromq libzmq lib0mq
  IMPORTED_TARGET
)

Information about ZeroMQ will be stored in an imported target named PkgConfig::ZeroMQ, which can be linked to executables or libraries.

✦

Related Source Code

✦

zmq_client.cpp

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <zmq.h>

int main() {
  void *context = zmq_ctx_new();
  void *requester = zmq_socket(context, ZMQ_REQ);
  int rc = zmq_connect(requester, "tcp://localhost:5555");

  if (rc != 0) {
    perror("Failed to connect to server");
    return 1;
  }

  while (true) {
    char buffer[] = "Hello";
    zmq_send(requester, buffer, sizeof(buffer), 0);

    char reply[10];
    zmq_recv(requester, reply, sizeof(reply), 0);
    printf("Received: %s\n", reply);
    
    sleep(10);
  }

  zmq_close(requester);
  zmq_ctx_destroy(context);

  return 0;
}

zmq_server.cpp

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <zmq.h>

int main() {
  void *context = zmq_ctx_new();
  void *responder = zmq_socket(context, ZMQ_REP);
  int rc = zmq_bind(responder, "tcp://*:5555");

  if (rc != 0) {
    perror("Failed to bind socket");
    return 1;
  }

  while (1) {
    char buffer[10];
    zmq_recv(responder, buffer, sizeof(buffer), 0);
    printf("Received: %s\n", buffer);

    zmq_send(responder, "World", 5, 0);
  }

  zmq_close(responder);
  zmq_ctx_destroy(context);

  return 0;
}

Build the project and execute

$ mkdir -p build
$ cd build
$ cmake ..
$ cmake --build .

Execute the results of the two generated processes:

Finally, I wish everyone to become stronger!!!